A commercially-available support arm has a pair of telescoped sliders and sequential latch structure, generally as shown in the Anderberg et al. U.S. Pat. No. 4,042,266. The Anderberg patent has a sequencing latch which is caused to sequence between a latch position and an unlatched position. This is effected by relative movement between the sliders and contact of the sequencing latch with a stop boss and coaction with the edges of a slot in one of the sliders. Full extension of the sliders relative to each other results in positioning the sequencing latch in a latch position, with a slight retraction of the sliders holding the sequencing latch in latch position. A succeeding full extension of the sliders causes pivoting of the sequencing latch whereby it may move to an unlatched position.
With the structure as shown in the Anderberg et al. patent, it is possible that the sliders of the support arm can be moved to full extended position, as when a strong wind acts on the window sash. As a result, the sequencing latch will be released from latch position for movement to unlatched position whereby the sliders of the support arm can move to a full contracted position enabling the window to slam shut. Because of this, in some areas, a building code has been established that prevents the use of a support arm of the type shown in the Anderberg et al. patent.